1. Field of the Invention
The present invention relates to wireless communications and particularly to radio frequency components for use in mobile communication terminals such as mobile phones and wireless communication terminals such as wireless LAN, which feature increased function, high integration, reduced size and low price.
2. Description of the Related Art
With the growing tendency towards more compact wireless communication terminals, there is demand for radio frequency components for wireless communication terminals that fit into a smaller packaging area. Conventionally, circuit of radio frequency parts have been divided into several blocks by function and the blocks have been manufactured separately as modules while efforts have been made to improve reliability, reduce size and increase integration for each module. For example, methods of heat dissipation in power amplifier (hereinafter referred to as PA) modules including power amplifiers as heater elements are disclosed in JP-A No. 27570/1997 and JP-A No. 147349/1995.
In recent years, JP-A No. 8584/1997 and JP-A No. 266546/1999 disclose techniques which produce more compact radio frequency components with higher integration in function by combining modules which would be separately manufactured in the former methods.
PA requires a heat dissipation structure because it consumes much electric power and generates heat. For this reason, various PA module structures for effective heat dissipation are disclosed: one example is a multilayer substrate which has, on its surface layer, an electrically isolated metallized layer or a metallized layer connected to a grounding layer (JP-A No. 147349/1995) and another example concerns a structure of a substrate in which the almost whole surface of the ceramic substrate is covered with a metal layer and through holes for heat dissipation are uniformly distributed almost all over the substrate (JP-A No. 27570/1997).
However, these conventional techniques have the following drawback: in a module which integrates a power amplifier and a device whose operating characteristics vary with rise in temperature, namely a device having sensitive temperature dependence of characteristics, on a substrate, the influence of the heat generated by the PA on the device having sensitive temperature dependence of characteristics is not taken into consideration, or though it is taken into consideration to mount a PA and a device having sensitive temperature dependence of characteristics together in a module, attention is not paid to the fact that part of the heat is conducted in the module substrate and then to the above-said device having sensitive temperature dependence of characteristics.
Therefore, in the conventional techniques, when a device having sensitive temperature dependence of characteristics is mounted together with a power amplifier on a substrate, the fair distance between both the devices was needed to avoid the influence of the heat generated by the power amplifier. Furthermore, a deterioration in electrical characteristics which is caused by change in characteristics with temperature rise has been unavoidable. For this reason, it has been impossible to produce a compact, high performance radio frequency module in the form of both a power amplifier, which generates heat, and a device having sensitive temperature dependence of characteristics are mounted together.